Pneumatic counterbalance

ABSTRACT

A pneumatic spring counterbalance extensible link including a closed end cylinder with an end connector a piston and rod assembly within the cylinder and maintained therein by the crimped over end portion of the cylinder retaining a rod bushing and rod to cylinder seal. The cylinder is pressurized prior to assembly of the complete piston and rod into the cylinder. The piston assembly includes orifice by-pass arrangements either in the piston periphery or in a piston ring, and the piston may include a fail-safe provision in the event the orifice is clogged. A crimping die assembly is used in assembling and completing final assembly of the counterbalance components while simultaneously maintaining the link in a pressurized environment, utilizing sealed arrangement between the crimping dies to maintain pressurization of the interior of the dies and the counterbalance components prior to assembly of the components. A dual force embodiment of the counterbalance unit is disclosed and utilizes a floating sealed piston below the main piston and rod assembly entrapping pre-charged gas in the space between the floating piston and the closed end of the cylinder.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 122,850,filed Feb. 20, 1980 (now abandoned).

BACKGROUND OF THE INVENTION

Pneumatic counterbalance units have come into widespread use in recentyears, being used on various automotive components such as hoods, trunklids, hatch backs and on other items such as machine covers, doors andhatches. Such pneumatic counterbalances are rather simple pneumaticpiston/cylinder arrangements having a bleed by-pass through or past thepiston similar to shock absorbers and oleo struts used on vehicles andair craft for many years. The well-known principle of operation is basedon differential pressure resulting from the differential in crosssection areas of the two chambers within the cylinder caused by thepiston rod on one side of the piston which reduces the area on that sideof the piston. Pneumatic counterbalance units, prior to this invention,have been pressurized subsequent to assembly, past the shaft seal, orthrough a fill valve or a fill port which is sealed afterpressurization. Prior art units utilize orifice bleed passages throughthe piston or through the piston rod from one side of the piston to theother side and more sophisticated units have a valving device whichvaries the bleed rate depending on the direction of movement of thepiston. Other forms of counterbalance devices provide a dual force byusing a supplemental compression coil spring which becomes effective atan intermediate position of the piston rod retraction stroke.

Examples of prior art counterbalance units can be seen in the followingU.S. Patents: U.S. Pat. No. 1,994,722 to O. W. Landerslager forResilient Device; U.S. Pat. No. 2,774,446 to Bourcier de Carbon forShock Absorbers: U.S. Pat. No. 2,788,867 to A. R. Causse for ShockAbsorber; U.S. Pat. No. 3,207,498 to E. Wustenhagen et al. for GasSpring; U.S. Pat. No. 3,222,047 to F. Tuczek for a Pneumatic SuspensionUnit; U.S. Pat. No. 3,589,701 to D. W. Gee for Vehicle Suspension (GasSpring); U.S. Pat. No. 3,856,287 to Freitag for Piston Rod Seal ForAdjustable Pneumatic Spring; U.S. Pat. No. 3,868,097 to P. H. Taylor forLiquid Spring; U.S. Pat. No. 3,913,901 to W. Molders for ResilientSupportng Column; U.S. Pat. No. 3,963,227 to W. Molders for Gas Springwith Duel Damping; U.S. Pat. No. 4,030,715 to H. O. Duran for PneumaticShock Absorber; U.S. Pat. No. 4,064,977 to D. F. Taylor for FluidAmplifier Shock Absorber having De Laval Nozzle; U.S. Pat. No. 4,098,302to Freitag for Method for Charging Pneumatic suspension Element; andU.S. Pat. No. 4,108,423 to J. J. Skubal for Gas Spring. Most of theforegoing patents disclose various types of piston unit orifices and ofdifferent kinds of seals between the piston rod and cylinder, some beingplurality O-rings or flat washers or a combination of both kinds andsome, e.g., Taylor and Duran use chevron seals. Duran shows ananti-friction ring on the piston with plural peripheral notchesproviding free-flow by-pass of fluid. Some disclose methods ofpressurizing, e.g., De Carbon shows a valved inlet; Tuczek shows amultiple inlet system with lines and accumulators; Freitag U.S. Pat.Nos. 3,856,287 shows a ball check valve; and Freitag U.S. Pat. No.4,098,302 charges gas and liquid past the seals. The Taylor U.S. Pat.No. 3,868,097 teaches a structure and method of assembly for a liquidspring.

SUMMARY OF THE INVENTION

This increase of use of pneumatic counterbalance units in consumer itemshas required increased production which can result in lack of qualitycontrol, e.g., manufacture requires pressurization by various techniquesof introducing gas into the cylinder following assembly and results inlack of accurate control over the requisite force needed for specificapplications. By the present invention a method and tool structure hasbeen developed to make a gas spring counterbalance and includespressurization within a crimping die assembly, just prior to completelyinserting the piston and rod assembly, and maintaining thepressurization during crimping of the cylinder. This results in veryaccurate quality control of the pressurization of completed units. Aunique die assembly was developed to accommodate the method of assembly.

Further developments included a different shaft seal arrangement andproviding extruded piston rings with preformed peripheral orificecontrol grooves and specially constructed piston rings withbi-directional by-pass and metering orifices to control linkageextension and retraction speeds.

To avoid the detrimental aspects of the extensible link becoming a fixedlength link should the metering orifice become clogged, a fail-safefeature has been developed to release the piston seal if the extensionforce exceeds a certain value. Also it is desirable in someinstallations to have a dual force capability in the counterbalanceunit. To solve this problem and avoid use of mechanical springs whichcan break or loss their spring force over a period of extended use, afloating piston concept was developed. Such a floating piston ispre-inserted and entraps gas in a lower chamber within the cylinder andits assembly and pressurization can be accommodated by the assemblytools and method of this invention.

OBJECTS OF THE INVENTION

A primary object of this invention resides in the provision of a novelpneumatic counterbalance link. The link is pressurized before and duringthe assembly step. The piston rod is sealed by a large O-ring or theequivalent which also seals against the cylinder and end bushing.Unidirectional seal rings, such as a cheveron seal, can be used ifdesired. Several novel embodiments of metering orifices across thepiston in the counterbalance combination unit include a preformed radialorifice groove in a piston flange, a pre-formed peripheral meteringgroove in an extruded piston ring or providing pre-formed meteringgrooves with correlated by-pass grooves in an O-ring held betweenaxially spaced piston flanges. Use of grooves in the piston ring toprovide the by-pass orifices and the metering orifices results in anadvantage over the apertured type orifices because the grooves willinherently self clean as the stroke is reversed and the ring moves awayfrom engagement with the piston flange. Resiliency of the O-ring resultsin flexing of the grooved areas of the O-ring and aids in eliminatingany contaminants or clogging. The piston flanges enable provision of afail-safe structure which is accomplished by controlled thickness of allor a portion of one of the flanges enabling failure by at least apartial destruction of the flange under pre-calculated applied force,resulting in eliminating the orifice controlled bleed past the pistonbut retaining the basic pneumatic counterbalance action of thecounterbalance link.

A further object of this invention resides in the provision of a novelmethod of assembly of pneumatic counterbalance units wherein thecomponents of the unit are positioned within crimping die tools in acrimping press with a small quantity of oil for lubricationpre-introduced into the cylinder component; the die parts with thecomponents of the unit are moved toward assembly; the die tool partsengage and provide a sealed compartment surrounding all components ofthe counterbalance unit. At this stage of assembly the die toolcompartment is pressurized by gas (e.g., air or nitrogen) under pressurethrough valve controlled pneumatic pressurizing connections from apressure source. While pressurized the press movement continues, thecrimping die parts move closer and the piston assembly parts includingthe rod seal and the end bushing move into the cylinder entrapping aquantity of pressurized gas within the cylinder. As the press actioncontinues, the open end wall portion of the cylinder is crimped inwardby the crimping die tool which retains the bushing, seal, rod and pistonin the cylinder and completes the assembly. Via suitable valve control,the sealed die compartment is vented, pressurization is released, thepress is reversed, the tools part and the completely assembledcounterbalance unit is removed.

As further objects of the invention, the same assembly method can beused to assemble a dual force counterbalance unit, which will include afloating peripherally sealed piston in the cylinder below the rod andprimary piston assembly. The floating piston component can be carried onthe bottom of the primary piston, adhered thereto by magnetic force orby use of a sticky substance, such as grease, or the like. As the dieparts move toward each other and create the sealed compartment aninitial pressurization of the compartment is caused, and the floatingpiston is introduced into the cylinder to a point which accomplishes asealed relationship with the cylinder, whereupon the die compartment issubjected to higher pressurization, the floating piston separates fromthe primary piston and moves into the cylinder to an intermediatelocation of equalization of pressures on both faces and an additionalsmall quantity of oil for lubrication is introduced into the cylinder ontop of the floating piston. Continued movement of the press and crimpingdies completes the assembly of the piston and rod into the cylinder andcrimps the cylinder, followed by removal of pressurization, parting ofthe die parts and removal of the completed unit.

Still another object of the present invention resides in the provisionof novel apparatus to accomplish the combination single stroke assemblyand pressurization of a pneumatic counterbalance unit. In conjunctionwith this object is the provision of a novel crimping die tool set foruse in a machine press including jig structures to maintaincounterbalance components in pre-assembly positions and having structureto provide a closed sealed cavity around the counterbalance componentstogether with a system to controllably pressurize the de-pressurize thecavity during the final stages of assembly of the counterbalance unit. Afurther novel feature resides in provision for pressure injection of apredetermined quantity of lubricating oil into the cylinder afterpressurization of the die cavity. This feature can be used in introduceoil into the bottom of the cylinder as well as on top of the floatingpiston.

Further novel features and other objects of this invention will becomeapparent from the following detailed description, discussion and theappended claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred structural embodiment of the apparatus and variousembodiments of the pneumatic counterbalance of this invention aredisclosed in the accompanying drawings, in which:

FIGS. 1-4 illustrate apparatus in accord with this invention by whichthe inventive method can be carried out to assemble and pressurize acompleted pneumatic counterbalance unit, FIGS. 1, 2, 3 and 4 showingrespective progressive stages and positions of the press heads, crimpingdies and counterbalance components to final assembly of the inventivecounterbalance unit;

FIG. 2A is an enlarged detail section taken on line 2A--2A of FIG. 2through the open end wall of a counterbalance cylinder component priorto assembly;

FIG. 5 is a partially sectioned elevation view of a complete pneumaticcounterbalance link unit according to this invention;

FIG. 6 is an enlarged cross section detail of the unit of FIG. 5 showingthe shaft seal, the shaft, the piston and the piston ring in itsmetering position when the link is being extended;

FIG. 7 is a view similar to FIG. 6 but showing the piston ring in theby-pass flow position which occurs when the link is being retracted;

FIGS. 8 and 9, respectively, a plan view and a cross section view takenon line 9--9 of FIG. 8, show the shape and groove details of the pistonring used in the unit of FIG. 5;

FIG. 10 is a further embodiment of a counterbalance unit which includesthe same components shown in FIG. 5-9 and in addition includes afloating piston to provide a dual force counterbalance link;

FIG. 11 is an enlarged detail section of the unit in FIG. 10 showing theprimary piston and the floating piston positioned in the overloadsecondary force condition;

FIGS. 12, 13, 13A and 14 are somewhat schematic depictions of stages ofassembly of a dual force counterbalance link such as shown in FIG. 10;

FIG. 15 is a schematic depiction of a completely assembled andpressurized dual force unit with the primary piston spaced from thefloating piston in a normal force condition;

FIG. 16 is a schematic depiction like FIG. 15 but illustrates the twopistons engaged and disposed in an overload force condition;

FIG. 17 is a further embodiment with a modified piston assembly withmetered orifice extruded in the outer periphery of the piston ring;

FIG. 18 is a plan view of the cup washer portion of the piston assemblyshown in FIG. 17;

FIG. 19 is a plan view of the extruded piston ring of the pistonassembly shown in FIG. 17;

FIG. 19A is a plan view of a modified piston ring;

FIGS. 20, 21 and 22 are detail section views illustrating extension,retraction and neutral conditions of a still further embodiment of apiston assembly;

FIG. 22A is a plan view of the upper piston washer of the FIG. 20device; and

FIGS. 23 and 24 are detail views of a further piston ring moldedembodiment with the metering orifice provided as a groove molded in thering.

GENERAL DESCRIPTION

The various aspects of the invention herein include articles known aspneumatic or gas springs, which for convenience can be referred to ascounterbalance links, as well as an apparatus and method for making thearticles. Representative embodiments of the counterbalance links areseen in FIGS. 5, 10 and 17 as well as in various other detail views.FIGS. 5 and 10 of the original Patent Drawings are full scale of actualunits.

The first portion of this description will be directed to the apparatusfor making (or assembling) the counterbalance links but initiallyreference is to FIG. 5 where is shown a representative embodiment of acounterbalance link 30 having a cylinder 32 whose length will bedetermined by the kind of equipment with which the unit is used. Withinthe cylinder is a piston assembly 34 which separates the cylinder intotwo compartments which are filled with gas (e.g., air, nitrogen or someother inert gas) under pressure. The piston assembly includes a freefitting piston 36, a piston ring 38 and the piston rod or shaft 40secured at one end 42 to the piston 36 as by swaging over or rivetingthe end at 44. These pneumatic counterbalance units, particularly inautomotive installations are often pressurized up to around 2000 psi gaspressure. Pressures can be higher or lower depending on theinstallation. A counterbalance unit with a piston rod havingapproximately 0.10 inch² cross-section area will provide a 5 poundextension force when the cylinder is pre-pressurized at approximately 50psi, and a 200 pound force when pressurized at 2000 psi.

The piston shaft 40 projects out through one end 48 of cylinder 32, theother end 50 of which is closed, as by welding a disc 52 thereto. Theprojected end of shaft 40 has a connector link 54 rigidly securedthereto, as by screw threads or welding, and a second connector link 56is secured to the cylinder closed end 50, as by screw threads orwelding. Within the cylinder, shaft 40 passes through a large O-ringseal 58 and a shaped bushing 60 which has a free close-fit around theshaft 40 and within cylinder 32. With the open cylinder end 48 crimpedat 62 the bushing 60 provides an end stop abutment for piston movementcushioned by the O-ring seal 58. Internal gas pressure keeps the seal 58and bushing 60 in the end position against the crimped end of cylinder32. As shown in FIGS. 2-4, a pre-determined small quantity of oil 64,e.g., 3-4 cc is placed into cylinder 32 prior to assembly and provideslubrication for the piston ring and the large O-ring seal 58. Unit 55represents an attachment clip and is not per se a part of thisinvention.

Suitable materials for the various components can be mandrel drawnhydraulic steel tubing for the cylinder, sheet steel for the end disc,the piston shaft is hardened, chrome plated steel, the bushing can bemade from aluminum or steel, the O-ring is elastomeric, e.g. rubber orplastic, and the piston is made from aluminum. As will be described indetail, the piston and ring components can be and are preferably madefrom various other materials depending upon the configuration ormodification of design. The piston and its ring, as are true ofpneumatic springs, are constructed to provide controlled by-pass flow ofgas from one side of the piston to the other side. There is a relativelyfree flow by-pass provided during the retraction or compression strokeand an "orifice" metered flow of gas past the piston during theextension or expansion stroke.

ASSEMBLY APPARATUS

Turning back now to FIGS. 1-4, the apparatus for assembling thecounterbalance units as seen in FIGS. 5 and 10 includes a specialcrimping die tool set fastened to the head 70 and bed 72 of a machinepress, which can be any known kind readily available in machine shops.The crimping die tool has upper 74 and lower 76 assemblies which will beaffixed respectively to the head and bed of the press and in workingalignment as shown in FIGS. 1-4. In the following description of thetool apparatus and the method of assembly of a counterbalance link,reference will be made to counterbalance link 30 and its referencedcomponents as shown in FIG. 5.

FIG. 1 shows the upper and lower crimping die assemblies 74 and 76fastened to the press. The crimping die set is constructed to enableassembly, pressurization and crimping of the work piece (counterbalancelink) in one operation, and the upper and lower die assemblies will sealwith one another via a dynamic gas tight seal, such as an O-ring, duringan initial pressing movement of the press head, to enclose thecomponents, during the remainder of the assembly operation, within apressurized gas-tight chamber.

The upper die assembly 74 has a steel base 78 with a counterbore 80sized to receive the shaft 40 of the piston and shaft subassembly. Base78 also has a large counter-bore 82 the outer portion 84 of which isthreaded and receives an externally threaded die holder sleeve 86 whichhas an inner end 88, having an outer circumferential groove 90 carryinga sealing O-ring 92, which spigots and seals in the base counterbore 82.Inset into and seated within the inner end of the die holder sleeve 86is an upper crimp die 94 made from tool steel. Carried within the die 94and seated in the upper end is a sleeve insert 96 through which thepre-assembled piston and shaft assembly is inserted with a close slidingfit. The insert sleeve 96 projects downward within the confines of thedie crimping face 98 a sufficient distance to keep the bushing 60 ofpiston and shaft assembly away from the crimping surface to permitspacing for the crimping operation on the cylinder end 48.

Note: If a flat end connector link 54 is pre-welded to the projected endof shaft 40, then the crimp die 94 will have to have dimetral clearanceslots 100 and the sleeve insert 96 will also have to be slotted as at102 to provide clearance for the connector link to pass through and upinto the counterbore 80. The latter can be accomplished by making thesleeve insert in two parts. The pre-assembled piston and rod assembly isheld in the upper die assembly with a low force which can beaccomplished by a permanent magnet 104 fixed at the base of counterbore80.

The lower die assembly 76 includes a sleeve shaped base part 110 fixedto the press base 72 and upstanding in coaxial alignment with the upperdie assembly 74. The upper end 111 of the lower die base is dimensionedto be received within the upper holder sleeve 86 and during the initialwork stroke of the press will telescope into the lower end of holdersleeve 86 and be sealed thereto by an O-ring 112 maintained in an outercircumferential groove 114, as shown in FIG. 3. An intermediate portion115 of the base sleeve 76 is externally threaded and carries a largestop nut 116 used to provide a limit stop for the press stroke, as shownin FIG. 4.

Interior 118 of sleeve 110 is cylindrical and made to have a close loosefit with the subassembled counterbalance cylinder 32 which ispre-inserted, base down, into the die part 76. When so inserted,cylinder 32 rests against a steel plug insert 120 situated in the bottomof sleeve interior 118 and seated against the press bed. Plug 120 isexternally grooved and carries an O-ring seal 122 which seals againstthe die sleeve interior 118. Just adjacent the top of plug 120, thelower die sleeve is radially tapped to receive a pressure line fitting124 from a gas source 126 under pressure via fluid controls 128 which ina pre-determined sequence will pressurize and depressurize (vent) thecrimping die assembly. An alternate location for the pressurized gasconnection can be in the upper die base 78 as shown in phantom line at132.

FIG. 1 shows a modification to the die set where an oil passage 133 isformed in the upper die holder sleeve 86 and a unit 134 consisting of anoil pressurizing pump is connected thereto to introduce a smallpre-determined quantity of oil under pressure through a directed orifice135 into a cylinder component when the upper and lower die assembliesare sealed and pressurized.

Shown in FIG. 2, a counterbalance cylinder 32 which includes a smallquantity, e.g., several cc of lubricating oil, is placed into the lowerdie sleeve interior 118 so its closed end is resting on plug 120. If aflat connector link 56 is welded on the end of cylinder 32, a slot 130in plug 120 will receive the connector link. The open end ofcounterbalance cylinder 32 projects above the top end of the lower diesleeve 110 as seen in FIG. 2.

OPERATION OF APPARATUS AND METHOD OF ASSEMBLING COUNTERBALANCE LINK

Using the crimping apparatus previously described and with the press inthe inoperative open condition (FIG. 1), a cylinder component 32 isplaced in the lower crimping die assembly 76 and a sub-assembled pistonassembly with piston 36, shaft 40, seal 58 and bushing 60 is placed into the upper die assembly 74 so the components are disposed as shown inFIG. 2. The press work stroke is then initiated, bringing the upper dieassembly 74 down toward and into engagement with the lower die assembly76 to the intermediate relationship shown in FIG. 3 where the O-ringseal 112 engages and seals against the inner surface of the upper dieholder 86. At this precise stage, the interior of the engaged die partsis a sealed cavity, all sub-components of the counterbalance link areinside that sealed cavity, and the cavity is pressurized with a suitablegas under pressure. The pressure will be determined by the nature of theintended use of the counterbalance link. It will be from several timesatmospheric pressure up to at least 2000 psi and if desired above 2000psi. Most requirements will be satisfied by pressures from 400 to 2000psi which can be accommodated by components of gas pressurized devices.

At this stage or instant in the press stroke, the charge of gas in thecavity is a specific predetermined quantity and pressure and will be thesame for every work piece being made. As the press continues its stroke,the projected piston, and the O-ring 58 enter the cylinder 32. Shown inthe detail FIG. 2A, the internal peripheral edge of the open end 48 ofcylinder 32 is chamfered with a durable entry chamfer of 15° and 45° tofacilitate introduction of O-ring 58 into the cylinder. At the pressstroke point where O-ring 58 seals against the inner cylinder surface, apredetermined quantity of pre-pressurized gas is trapped inside thecylinder and is compressed still further by continued operationalmovement of the press and the crimping dies. Final movement of thepress, as shown in FIG. 4, causes the inner crimping face 98 of theupper crimp die 94 to abut the cylinder end 48 and pressure crimp thewall end inward to complete the final assembly operation of thepneumatic counterbalance link.

As the press starts on its return stroke, the pressurizing line controlswill be operated manually or automatically in a known manner to shut-offthe pressure flow and to vent the die assembly and release pressure fromthe cavity as the press is moving the die assemblies toward the unsealedcondition, so that the cavity is not pressurized when the cavity becomesunsealed. The completed workpiece is removed and the cylinder repeated.

METHOD APPLIED TO ASSEMBLE DUAL FORCE COUNTERBALANCE LINK

The same apparatus just described relative to FIGS. 1-4 can be utilizedto assemble a modified version of the single force pneumaticcounterbalance link, i.e., it can be used to assemble, pressurize andcrimp a dual or plural force gas spring, which will be hereinafterdescribed.

A dual slope output force is employed in some pneumatic springspresently being used to "pop" open an automotive trunklid apredetermined amount of about two inches. The lid will then stay at thatposition until manually opened for another amount where the pneumaticspring linkage geometry is such that the lid will open and stay open byspring force only. Prior to the present invention, dual force has beenaccomplished by the addition of a small compression spring installedinto the pneumatic spring cylinder prior to insertion of the piston androd assemby. In normal use when that pneumatic spring is compressed, anadditional force must be applied for the final portion of the compressedstroke when and after the piston has contacted the compression spring.

This invention accomplishes the dual slope feature pneumatically byincorporating a floating piston in the pneumatic spring cylinder. Whenthe piston, which is fixed to the piston rod, is in engagement with thefloating piston the output force will increase at a higher rate.

FIGS. 10 and 11 show the dual force output counterbalance link 136 witha floating piston 170 having an elastomeric sealing O-ring 172. Link 136and components are hereinafter more specifically described but basicallyinclude similar parts and construction as in the unit 30 of FIG. 5, plusa floating piston. With such a floating piston the cylinder encompassesone sealed compartment 174 behind piston 170 and the two compartments,one on each side of the primary by-pass piston as is true in unit 30.

FIGS. 12-16 depict the method of assembly of the dual forcecounterbalance link 136 in a somewhat schematic manner.

FIG. 12, corresponding to FIG. 3, shows the initial pressurization mode,where the cylinder contains the small amount of lubrication oil 64previously mentioned with neither of the piston yet inserted into thecylinder. The floating piston 170 may be temporarily attached to thefixed piston assembly 140 by magnetic attraction (e.g., small magnet176) or by some other controlled method such as sticky grease. The crimpdie chamber is initially pressurized to a value which is below the finalpressure.

FIGS. 13 and 13A depict the positions where the press has moved toaccomplish insertion only of the floating piston to a sealed conditionand then (FIG. 13A) is backed off slightly to remove the fixed pistonfrom the floating piston, whereupon the crimp die chamber is immediatelysubjected to the higher final pressure and and predetermined quantity ofoil 178 injected via the orifice 135 shown in FIG. 1.

FIG. 13A depicts the disposition of components after finalpressurization has freed the floating piston from the fixed pistonconnection (the magnetic holding force being lower than that holding thefixed piston in the upper die assembly) and displaces the floatingpiston 170 into the cylinder compressing the gas ahead of it intocompartment 174 until it equals the final pressure and a balance ofpressure will exist across the floating piston 170 and the smallquantity of oil 178 has been introduced on top of the piston 170. FIG.14 shows the upper die assembly moved down to introduce the fixed piston142, O-ring 162, and bushing 164 into the cylinder 138. Final assemblyis accomplished by the same further steps as described with respect toFIGS. 1-4.

FIG. 15 depicts normal operation where the fixed shaft piston 140 movesin and outer without contacting the floating piston 170. The outputforce is equal to the internal pressure acting on the piston rod area.

FIG. 16 depicts the overload force mode where the fixed piston 140contacts the floating piston 170. Displacing the piston rod 146 into thecylinder 138 displaces the floating piston 170 which is now in contactwith the fixed piston assembly 140 and both pistons move together. Theoutput force on rod 146 is equal to the normal gas pressure acting uponthe piston rod area and the differential pressure across the floatingpiston. Due to the large area of the floating piston 170 and therelatively small gas volume ahead of it, the output load slope willincrease and at a much higher rate. Another desirable feature of theoperation in the overload mode is the elimination of piston orificedampening because there is no flow across the fixed piston. This willassist the desired initial "pop" open of an automotive trunk lid uponunlatching.

PNEUMATIC COUNTERBALANCE LINKS

This invention includes a gas spring or pneumatic counterbalance link ashas been previously described. The link can be a single output link 30as described with reference to FIG. 5 or a dual output force link 136 ashereinbefore described with reference to FIGS. 10 and 12-16. In eithercase the fixed piston assembly, as illustrated, includes a constructionwhich provides essentially free by-pass flow of gas across the pistonduring a retraction or compression stroke and a metered orifice flowduring the extension or expansion stroke. Several modified versions ofthe cooperation piston and ring assemblies are shown herein, any of theembodiments can be used in the single force link or the dual outputforce link. Depending upon the application of use of the counterbalance,free flow or metered orifice flow across the piston can be in thereverse of that just described, or free flow, or metered flow, could beprovided for both directions of the piston stroke meterly by reversingthe installation of the piston ring or changing its configuration.

In FIGS. 5 through 9, the piston assembly is a single piece spool 36with a thick flange 180 disposed toward the crimped end 62 of cylinder32 and a thin flange 182 disposed toward the cylinder closed end 50.Piston 36 is slipped onto the reduced diameter end 42 of piston shaft 40and the end 42 then swaged over or riveted to securely fasten thepiston. The diameter of thick flange 180 is predetermined to providesufficient clearance from the cylinder wall to enable unrestricted gasflow through the annular space 184. The diameter of the thin flange 182also has sufficient clearance to enable unrestricted flow of gas throughannular space 186. Dispsoed within the groove of piston spool 36 is aspecial molded piston O-ring 38 made of flexible elastomeric material,such as synthetic rubber or plastics to permit stretching when the ringis slipped over the flanges. The piston spool can be made of two parts,as shown in FIG. 11, to permit the piston O-ring 38 to be molded from asynthetic plastic material which need not be stretchable, it can beassembled between the two parts of the piston. In either event, thepiston O-ring 38 will have an inner diameter sufficiently larger thanthe base diameter 188 of the piston groove, and will be provided withseveral (4 shown) slots 190 on one side slightly less than 1/2 diameterdeep, to enable free flow by-pass openings for gas to flow across thepiston 36 when being moved in a retraction operation as depicted byarrows in FIG. 7. On the other side of the O-ring is a single, formed(preferably pre-molded) orifice groove 192 which serves to provideorifice metered flow during the expansion stroke as shown by arrows inFIG. 6. In a typical installation such as FIG. 5, piston ring 38 is0.645 inch diameter with a cross-section radius of approximately 0.100inch and the cross-section orifice by-pass is 0.0006 sq. inch. The roddiameter is 0.314 inch, the cylinder I.D. is 0.620 inch and pistonstroke approximately 3.75 inches.

In FIG. 10, the unit 136 is the same and has similar components as thoseof FIG. 5, e.g., cylinder 138, piston assembly 140 with the fail-safepiston 142 made in two parts 142a and 142b to enable a synthetic plasticpiston O-ring 144 to be pre-assembled with the parts 142a and 142b onthe end of piston shaft 146. The piston ring 144 has the sameconfiguration as ring 38 and the piston 142 is staked or riveted at 150on the end 148 of piston shaft 146. Cylinder 136 has a closed end 154with end disc 156 and an open end 152. Connector links 158 and 160 arewelded to the shaft and cylinder to enable installation as desired.Large elastomeric O-ring 162 against the end bushing 164 provides acombination static cylinder seal, dynamic shaft seal and compliantpiston stop. The compliance will provide an additional cushion todecelerate extension movement and reduce noise at the end of the stroke.Crimped end 166 of cylinder 138 maintains the components ofcounterbalance unit 136 in assembly.

Unit 136 of course includes the previously described floating piston 170with its sealing O-ring 172 trapping a predetermined quantity ofpressurized gas between the piston 170 and the closed end of cylinder138.

Another version of the pneumatic counterbalance link, made asafore-described, is shown in FIG. 17 with details shown in FIGS. 18 and19. The link 200 includes the basis cylinder 202 with closed bottom 204and crimped end 205 and the piston and rod assembly with piston parts206 and 208, piston ring 210, shaft 212, chevron seal 214 and bushing216. The piston is made in two parts, a single flanged spool 206 and acupped washer 208 fitted together with piston ring therebetween andstaked on the end of the shaft 212. The I.D. of the piston ring 210 anddrilled orifices 218 in the inner portion of cup washer 208 serve toprovide free flow by-pass of gas in the retraction movement of thepiston. Piston ring 210 is cut from an extruded tube made from plasticmaterial such as "HYTREL" and incorporates an extrusion formed orificeby-pass groove 220 on the outer periphery of the ring. In thisembodiment when the cup washer 208 is used, the shaft and cylinder sealring 214 can be a chevron seal, with the cup washer flange abutting themid-section of the chevron seal to avoid damage to the seal lips at theend limit of the stroke. FIG. 19a is a modification 210' of the extrudedpiston ring 210 with orifice groove 220', and includes a plurality ofinternal ribs 222 which serve to coaxially locate the ring 210' on thepiston and facilitate assembly.

FIGS. 20, 21 and 22 illustrate a further embodiment in which a two partpiston 224 is used with a plain O-ring piston ring 226 whch has its I.D.spaced from the inside diameter of the piston spool 224. The upperflange part 227 (FIG. 22a) of the piston has free flow by-pass apertures228. The lower flange of the piston has a radial metering orifice slot230 formed therein as by coining. Retraction movement of the pistonpermits free flow of gas across the piston ring 226 as shown in FIG. 21,and extension movement of the piston results in orifice metered flow viaorifice groove 230 across the piston as shown in FIG. 20. FIG. 22 showsa normal neutral position of the piston at rest.

FIGS. 23 and 24 illustrate an alternate piston ring of molded rubber orplastic which can be used with the FIGS. 17 and 20 two part pistons. Thepiston ring 240 has single metering orifice slots 242 and 244, one oneach side of the ring. This ring can be installed with either faceagainst the downward flange and avoid erroneous upside downinstallation.

FAIL-SAFE PISTON

The counterbalance link has been developed to preclude the problem oforifice contamination by implementation of a feature which increases theorifice size when flow is reversed to facilitate the dislodging of anyentrapped contaminants. In the event that the orifice remainspermanently closed, a catastrophic failure of the counterbalanceassembly or supporting structure wil be precluded by a fail-safe pistondesign which allows a controlled failure of the piston ring supportingsurface thereby allowing free flow of gases in both directions. Thestructural integrity of the unit, however, is not compromised and thecounterbalance will continue to function without the rate controlledextension feature.

Contamination of the metering orifice will hydraulically lock the unitand such problems have been encountered particularly in units whichincorporate a drilled orifice. Should an orifice become clogged when thespring is on a vehicle there is a possibility of damage to a door,linkage or failure of the spring if the door is forced with the springhydraulically locked due to a clogged orifice.

Applicant's fail-safe piston design is shown in FIGS. 5-7. The righthand piston flange 182 will be weakened by making it thinner or byaddition of a failsafe notch. Normal operation and load carryingcapability will not be compromised since the loads with the pistonbottomed in the extended condition are carried by the thicker lefthandflange. Should the orifice become clogged and the door forceably openedthe piston forces will be applied to the right hand flange 182 with thefail-safe feature. An overload will deform the flange from the pistonallowing the seal to "blow out". Deformation of flange 182 under such acircumstance is depicted by phantom line 183 in FIG. 6. The pneumaticspring will continue to function after this fail-safe feature has beenactuated but operation will be without orifice controlled dampening.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:
 1. Apneumatic spring link comprising: a cylinder assembly with a closed end;a piston assembly in said cylinder with a piston shaft extending fromthe other end of said cylinder, a bushing on said shaft, an annular sealmeans around said shaft, a piston means with a piston ring, sealingagainst said cylinder, fixed on the end of said shaft; the other end ofsaid cylinder being crimp shaped to retain said bushing; said seal meansproviding a static seal against said cylinder, and a dynamic seal aroundsaid shaft; said piston means and piston ring providing means enablingmetered orifice by-pass flow of gas across said piston in one directionof stroke and a free flow by-pass fluid communication path across saidpiston means in the other direction of stroke; a predetermined smallquantity of oil being contained in said cylinder; said cylindercontaining a pre-determined quantity of gas under pressure; said pistonmeans having a spool shaped piston with flanges of less diameter thanthe I.D. of said cylinder to provide an annular free-flow space betweenthe piston flanges and said cylinder, and at least one of said flangesbeing deliberately made in a weakened condition as a fail-safe device todeflect and release said piston ring upon contamination clogging of saidmeans providing by-pass flow across said piston, and to thereby permitcontinued spring function without the metered orifice by-pass flow ofgas.
 2. A pneumatic spring link as defined in claim 1, wherein thefail-safe weakened piston flange is the flange closest to the closedcylinder end and said means enabling metered orifice by-pass gas flowacross said piston is operative during the extension stroke.
 3. Apneumatic spring link as defined in claim 1, wherein both flanges areweakened to provide a fail-safe device regardless of direction of strokewhen by-pass flow is prohibited by clogging.
 4. A pneumatic spring linkas defined in claim 1, 2 or 3, wherein said means enabling meteredorifice by-pass flow of gas across said piston during the extensionstroke and a free flow by-pass flow during the retraction strokecomprises a groove in one of the group consisting of the piston and thepiston ring, said groove being in the area of abutment between saidpiston and said piston ring which occurs during the extension strokewhereby the relative movement of the piston and piston ring into andaway from abutting engagement during extension and retraction providessaid groove with a self cleaning flow action.
 5. A pneumatic spring linkcomprising: a cylinder assembly with a closed end; a piston assembly insaid cylinder with a piston shaft extending from the other end of saidcylinder, a bushing on said shaft, an annular seal means around saidshaft, a piston with a piston ring, sealing against said cylinder, fixedon the end of said shaft; the other end of said cylinder being crimpshaped to retain said bushing; said seal means providing a static sealagainst the cylinder, and a dynamic seal around said shaft; said pistonand piston ring providing means enabling metered orifice by-pass flow ofgas across said piston during the extension stroke and a free flowby-pass fluid communication path across said piston during theretraction stroke; a predetermined small quantity of oil being containedin said cylinder; a predetermined accurate quantity of gas under atleast several atmospheres of pressure in said cylinder, having beenpre-loaded under pressure into said cylinder before, and maintainedunder pressure during, the final mechanical assembly steps of forcedinsertion of the shaft seal and bushing into the cylinder followed bycrimping of said other end of cylinder, whereupon said spring linkcontains and retains an accurately pressurized and predeterminedquantity of gas; said means enabling metered orifice by-pass flow of gasacross said piston during the extension stroke and a free flow by-passflow during the retraction stroke comprising a groove in one of thegroup consisting of the piston and the piston ring, said groove being inthe area of abutment between said piston and said piston ring whichoccurs during the extension stroke, whereby the relative movement of thepiston and piston ring into and away from abutting engagement duringextension and retraction provides said groove with a seal cleaning flowaction; and said piston being spool shaped with dual flanges, one of thespool flanges, the flange closest to the closed end of said cylinder,being made intentionally weak enough to destruct if said orifice by-passgroove becomes inoperative to cause the link to act as a fixed link. 6.A pneumatic spring link as defined in claim 5, wherein said weak flangeis made thin enough to deflect under a predetermined load tending toextend said shaft when said orifice by-pass groove is inoperative.